Hi!

To perform electrical lenght measurement You can use HP network analyzer with Time Domain transformation. But remember, to have good results You need analyzer with frequency range up to 20GHz. With this method is quite easy to decide where is connector and measure electrical lenght of coax cables.
To measure phase matching You need to have very good calibration. Calibration kits defined in network analyzers are not defined enough good. For example "thru" standard has zero delay offset. The best way is to take a close look at calibration standard definition in analyzer and if necessary modify them a little bit. It needs few calculations but all needed formulas You should find on the web or just contact HP.

HP 8753C can do your measurement if option 010 is installed.  If not, you cannot measure time domain, required for phase mesurement.  Without phase measurement you cannot compare phase.  You should know what frequency you want to make this comparison at, too. HP part number 85019B was a kit that would let you install this capability yourself.  Kit price in 1994 was $5300, when the 8753C was $27,500.

I'm looking into the phase matching (binning) of short semirigid cables using S11 on an 8720 with time domain.  Can I achieve 1 or 2 degree measurement accuracy at 20 GHz?  What is a good formula for resolution from bandwidth, IF BW, etc.?